Myxobolus supamattayai n. sp. (Myxosporea: Myxobolidae) from Thailand parasitizing the scale pellicle of wild mullet (Valamugil seheli).

A new myxosporean species, Myxobolus supamattayai n. sp., was isolated from wild mullet (Valamugil seheli) from the Andaman Sea, Thailand and described based on its morphology and molecular data. The myxosporean produced black plasmodia-like unique clinical sign on the skin with sporogonic stages and mature spores. Polysporous plasmodia, up to 2.5 mm in diameter, were found in epithelium tissue in the scale pocket. The spores measured 6.6 (6.2-7.0) μm in length, 6.5 (6.2-6.7) μm in width, smooth, and round board to ellipsoidal in valvular view. Spores were enclosed with intracapsular process which represents 5-7 and 11-12 in amount revealed in light microscopy and ultrastructure, respectively. The polar capsules were pyriform and of equal size, measuring 3.5 (3.4-3.6) μm in length and 2.0 (1.9-2.2) μm in width, with four to five turns of polar filament arranged perpendicularly to longitudinal axis of the polar capsule. In conclusion, this new species is entirely different from those previously described; however, this finding was assured by the partial sequence of SSU rRNA gene (1,666 bp) analysis that differed from all known species of Myxobolus Bütschli, 1882. The phylogenetic tree of the sequence data sets including those of freshwater and marine of Myxobolus spp. and the sister group (Henneguya spp.) was constructed to establish the relationship of this new species in Myxobolus clade and to explore its relations between their sister groups. Phylogenetic analysis indicated that a monophyletic group with Myxobolus spp. which infected mullet represents the newly formed species. These results suggested the presumably nearby evolution prospecting of Myxobolus species that were found in the same host.